fix: update soft block limit to 2MiB

[Jorropo]

This is needed because the 1MiB limit is the chunker limit, however the
actual blocks can be wrapped in protobuf which adds a small ~10 byte
overhead.

[Jorropo]

may 26 2022 discussion:
Need to add two tests:

• ipfs block get $(ipfs add --raw-leaves=false --chunker=size-$(( 1024 * 1024 )) 1MiBFile) | ipfs block put works. (non raw leaves blocks with 1MiB chunks include a ~10 bytes protobuf wrapping making them slightly too big, thoses blocks MUST pass, this is what this PR fixes)
• top down blackbox exchange test of 2MiB blocks.

[Jorropo]

Other possible solution if this drag on too much, revert 04e7e95 in 0.13.0 and move it to 0.14.0.

[lidel]

I'm moving this to 0.15: this needs end-to-end regression tests so we are not surprised when something changes deep in one of libp2p deps. We want tests for two cases:

• confirm two nodes exchange 2MiB block
• confirm two nodes are unable to exchange 2MiB+1 byte block

[BigLep]

What's the priority of this? What is motivating this work?

[Jorropo]

What is motivating this work?

1. There is edge cases when you use 1MiB without --raw-leaves you exceed 1MiB because the protobuf wrapper.
2. linux2ipfs use 2MiB raw leaves blocks and I don't like being annoyed when I use it.

[lidel]

This still needs tests described in #8968 (review)

[Jorropo]

I know, I didn't took time to wrote them yet.

[Jorropo]

confirm two nodes are unable to exchange 2MiB+1 byte block

I didnt do this because we don't really have consensus on this: ipfs/specs#331 (comment)